Under normal condition, the working principle of main thermostic bimetal in FTB1 SMCB is the same to the usual circuit breakers, it is used for overload tripping. when there is a short-circuit on a branch circuit breaker, the magnet core in the main current path would tilt the moving contact away from the fixed contact to break the circuit,thus producing the electric arc, and limiting the short-circuit current effectively.

In the maintime,the short-circuit current flow to the supplementary current path, a selective resistor and a selective bimetal are connected in series of the supplementary curret path, limiting the short-circuit current to a few hundred amps.

When the downstream circuit-breaker has tripped because of a short-circuit, the contact tips reclose automatically through a simple spring-type system,ensuring other unaffected branch circuits continue in operation.If a short-circuit occur between the FTB1 and the downstream circuit-breaker, another bimetal release enables short-time delayed tripping,ensuring the contact tips remain in the open position enabling isolating.

The FTB1 series operates selectively with respect to the combination with MCBs

MCB(B,C characteristic) FTB1(Characteristic E)

In A

20

25

32

40

50

63

80

100

10

T

T

T

T

T

T

T

T

16

T

T

T

T

T

T

T

20

T

T

T

T

T

T

25

T

T

T

T

T

32

T

T

T

T

40

T

T

T

50

T

T

63

T

Note: T represents total selectivity

Applications

Tripping characteristic

Exterior and dimensions

Visit our website http://www.southlandelectrical.com/itemdesc.asp?ic=GHB1070-NS or call 800-476-1486 or to order this Eaton Cutler Hammer GHB1070, 70 Amp, 277 Volt, Single Pole Circuit Breaker or any other parts! Southland Electrical Supply offers thousands of circuit breakers both new and reconditioned with a 1 year warranty. Our experts have 50 years of experience and are ready to help you get the part you need at the price you want.